Fun With Light

Polarized Light

I recently purchased a sheet of polarizing filter material so I could play with polarized light and show the effects to my granddaughter, Sophie.

Light propagates through matter by causing electrons within matter to oscillate. Electrons absorb light and oscillate as a result. Oscillating electrons then emit light. Light transmission proceeds through a series of absorption and subsequent emission events by one electron after another along the path of transmission. Molecules in the polarizing filter have a structure such that electrons can oscillate in one direction, say up and down, much, much easier than they can oscillate in a perpendicular direction, say side to side. When unpolarized light, oscillating in all directions, propagates through the polarizing filter, up/down oscillations get through much, much easier than side to side oscillations. Light exiting from the polarizing filter is, therefore, oscillating almost entirely in the up/down direction, and, thus, becomes mostly linearly polarized in the up/down direction. 

I found my laptop screen to be a good source of white light. For example, a blank new file in Microsoft Notepad looks like the first image below.

I probably should have known beforehand that laptop screen light is polarized, but I discovered it with the polarizing filter. The next image shows a piece of polarizing filter held so it lets laptop light through.

The next image shows the filter rotated 90 degrees, completely blocking light from the screen. So, laptop light is linearly polarized!

Next, I tried the well-known procedure of placing various plastic objects between the polarized laptop light source and a polarizing filter. I thought Sophie would like seeing how colors appeared like magic. For example, the next image shows an ordinary empty tape dispenser placed between the computer screen and the polarizing filter.

Next, I tried the bottom of a plastic McDonald's cup.

Sophie said, "Cool!" I was thrilled that she liked it! But what causes the colors? The light source is white, and the polarization filters alone don't cause colors to appear. It must be caused by the properties of the plastic items themselves and how they interact with polarized light.

The colored plastic material is birefringent. This means the internal molecular structure creates asymmetric conditions for the propagation of polarized light. (In other words, electrons can oscillate more easily in one direction than another.) In one particular polarization direction, say the x-direction, light travels fastest through plastic. If light is polarized in the y-direction, perpendicular to the x-direction, it travels slower through plastic than light polarized in the x-direction. This is equivalent to saying the index of refraction varies with polarization direction.

When polarized white light from the laptop enters the plastic it encounters molecular asymmetries mentioned above. Some component part of the incident polarized white light encounters regions where it travels fast, and some other component part encounters regions where it travels slower. The components get out of step and finally emerge combined from the plastic with an overall different exit polarization direction than the entrance polarization direction. The change in polarization direction depends on the wavelength of the light, therefore different colors change polarization direction by different amounts. So when we view the plastic object through a polarization filter that would block polarized laptop light, we don't see blackness. Instead, we see a range of colors where different wavelengths of white light have changed their polarization direction by different amounts.

I tried several other items with mixed results. Some looked very nice, like this protractor from my old college drawing kit.

The (broken) circle template was also interesting.

This French curve drawing tool was nicely colored.

I rummaged around the house looking for other plastic candidates. An old cassette tape case produced a good result.

Would an old CD case also show colors? Yes.

How about the plastic lid to a bathroom Q-tip dispenser?

I tried an empty sliced ham container.

The last item of this type was the cylindrical plastic tube of an "energy stick".

Colorful effects can also be achieved with overlapping clear "scotch" tape segments. Sophie and I enjoyed making some of these by placing tape strips on a clear plastic sheet. Fortunately, we had the kind of tape that works. I've heard some types of tape don't work. Different tape thicknesses change polarization directions by different amounts depending on wavelength, so wonderfully colorful arrangements result.

When the polarizing filter in front of an overlapping tape arrangement is rotated a nice kaleidoscopic effect results.

All these effects are well known. There's nothing new here except the fun we had when my granddaughter saw these for the first time.

 

A Little Solar Action

Two Sunspots

The Sun continues to slowly progress through its sunspot cycle minimum. After weeks of clouds, heat, humidity, and rain, a cold front finally blew through to clear skies and give a few days of wonderfully cooler temperatures and lower humidity. It was 74 degrees on August 24th when I set up my solar telescope to image two small sunspots.

The first image below is a 21-panel mosaic showing two modest sunspots to the right of center. Most of the solar disc is otherwise blank except for a wispy filament at the top left of the image. Two minor prominences are also visible. (Click on the image for a larger view.) 

Imagine the Sun without the two sunspots seen below. That's how blank the solar disc has been lately. This mosaic didn't work well. For some reason software would not align all the panels properly, so I had to crop out the misaligned pieces. Seeing was variable while recording the 21 segments, so there are blurry patches within the whole. 

The next image is a detailed close view of the two sunspots taken during a few moments of good seeing. At the top of the image sunspot 2720 shows a nice dipole structure. At the bottom of the image sunspot 2719 has disrupted surface features. Closely paired sunspots often have north/south magnetic polarity. Sunspot 2720 has its north and south poles aligned opposite to the polarity of sunspots we've been seeing up to this point as solar minimum approaches. This could signal the ending of the minimum phase. Maybe sunspot activity will very slowly increase over the next year.

Once all my equipment was operational I had only 50 minutes of clear sky before lots of fair weather clouds began to parade across the sky blocking the Sun again and again. The beautiful observing conditions were nice while they lasted.

Lava Covers Ahalanui Park

Hawaiian Lava Destruction

Recent Hawaiian volcanic eruptions and lava flows are happening near where we stayed in Pahoa during our December, 2011 visit to the big island. Our shoreline rental house was located only about 5 miles from the spectacular (fissure 8) lava fountain and the homes it obliterated. Some roads we used are now under impassable black lava, and one of the parks we visited recently disappeared under advancing molten rock.

One day in 2011 we drove along Route 137 to Ahalanui Park, a lovely small park along the coast featuring a natural, volcanically heated, spring-fed, warm water swimming hole next to the ocean.

Palm trees and a small grassy area preceded the swimming hole.

The main attraction was the swimming hole seen in the next four-panel panorama. (Click on the image for a larger view.)

The warm water pool opened directly into the ocean.

My 1.5 year-old granddaughter, Sophie, enjoyed the warm water with her Dad, Keegan.

My daughter, Ellen, did some snorkeling and snuggled little Sophie in a towel.

These beautiful scenes now remain only in photos and memories because lava has completely covered and obliterated Ahalanui Park. The next two maps from the US Geologic Survey (USGS) on July 12, 2018 show where ongoing lava flows eventually found their way to the sea and the park. (Click on the next two maps to see them at full size.)

Our rental house was located on the shoreline in the Hawaiian Beaches neighborhood seen at the top of the previous map. The actual location is just off the top of the map. We drove on Routes 132 and 137 to reach Ahalanui Park. The next picture from the USGS shows the lava-altered coastline where Ahalanui Park was located. The largest white plume near center is the park's former location.

An even more spectacular aerial USGS photo from July 14th shows glowing red lava and three bright white plumes from the approximate location of Ahalanui Park.

A more head-on view on July 15th shows the same three major plumes. The small pond, slightly inland, seen to the left of the plumes is approximately a half mile from the Ahalanui Park location.

Notice the significant expansive change of the coastline in the light pink Vacationland Hawaii area on the map above. Hawaii must be the only state with growing land area! Who owns the new land? Probably the state, of course. But if lava flows expand the shoreline immediately adjacent to privately owned land, does the property owner suddenly own more property?

This would be a fantastic time to visit Hawaii to see spectacular active lava flows, although I don't know how close tourists can actually get to the action. Many roads are blocked by lava, and authorities have probably erected barriers on other roads to keep people away. But the opportunities now are surely greater than what we experienced on our lava hike in 2011.
 

Beach Time

Outer Banks Fun

C likes nothing better than standing in the surf watching waves. C loves the sea.

The whole family spent lazy days on the beach.

Granddaughter Annabelle was happy to play in her pool and nap in grandma's arms.

Granddaughter Sophie did some reading. She was confident and exuberant in the water, even standing on the paddle board!

Sophie also enjoyed electric go karts with her Dad, Keegan.

Our beach house had a rooftop crow's nest which would have been ideal for stargazing if glaring neighborhood lights weren't assaulting my eyes from all directions. I walked to the beach to escape the lights, but without success. Houses along the beach felt compelled to light their back porches, so, even though there were no lights to the east over the ocean, sky views were not truly dark. The constellation Cygnus, the Northern Cross, was rising over the ocean in the following ten-second exposure made on the beach with my tripod-mounted phone camera. Lyra and Vega can be seen above Cygnus.

The next image was taken looking south along the shoreline. Lights from more heavily developed areas made a glow near the horizon. The Milky Way was washed out, but the constellation Scorpius was visible in the lower center. The bright object in the upper right is the planet Jupiter close to the star Zuben Elgenubi.

About 1.5 miles north of our beach house was the little town of Duck, home of an interesting variety of small shops. One morning we biked on sidewalks from our house into Duck to get donuts. Duck had its charms, but the traffic and crowding were sometimes overwhelming. One evening we got some ice cream from a shop called, Donuts on a Stick. Yes, they sold donuts on a stick, but they weren't just plain donuts. The donuts themselves were glazed and covered with sprinkles. Ice cream went on top of the donuts along with more toppings, whipped cream, and optional chocolate sauce. This insane caloric bomb was too much for me. It just made me laugh. The over the top extravagance of ice cream and donuts was balanced by another extreme - insect snacks!

Duck has a beautiful boardwalk that winds along the water of the Currituck Sound. As you progress along the boardwalk open areas alternate with small shops. We had a wonderful evening stroll on this boardwalk.

A pleasant warm breeze off the water enhanced peaceful scenes near sunset.

It's easy to understand why so many people vacation on the Outer Banks. 

Sand Dunes

Jockey's Ridge

Immediately after visiting the Wright Brothers National Memorial on North Carolina's Outer Banks during our recent vacation we drove three miles further south to Jockey's Ridge State Park, home of the tallest natural sand dunes in the eastern U.S. The walking path from the parking lot to the dunes began with a short, pleasant, shaded segment before opening up to a long, hot, sandy march under a blazing sun. The next picture shows the scene as we headed out toward the giant dunes. This panoramic view captures some of the enormous scale, but the image needs to be viewed at a larger size to see the full effect. (Click on the image for a bigger, more realistic view.)

We hiked to the top of the high dune seen in the upper left of the previous image. Of course, it's not easy walking on soft sand, so it was a long, slow slog, especially the final climb up the dune itself. Next is a panoramic view from the top of the high dune. This image might take a while to load. Once again, you should click on the image to view it in full size.

We feel fortunate at our age to be fit enough to hike out onto these dunes. C still looks fresh at the outbound limit of our hike.

Thank goodness for breezes, the same windy conditions that drew the Wright brothers near this locale for their glider experiments. Lots of hang gliders waited for favorable wind conditions at the top of the highest dune, and many kites were aloft.

A young girl took off for a short flight.

We watched hang gliders for a while. Then it was time to walk back. During the return hike heat and soft sand took a toll. We are both distance runners, however, so we knew how to pace ourselves and endure. The drinking fountain in the visitor center was a welcome relief. Afterward we were definitely ready for some dinner and air conditioning!